A universal mobile telecommunications system (UMTS) is a third-generation mobile communications system evolving from a global system for mobile communications system (GSM), which is the European standard. The UMTS is aimed at providing enhanced mobile communications services based on the GSM core network and wideband code-division multiple-access (W-CDMA) technologies.
In December 1998, ETSI of Europe, ARIB/TTC of Japan, T1 of the United States, and TTA of Korea formed a Third Generation Partnership Project (3GPP) for creating detailed specifications of the UMTS technology. Within the 3GPP, in order to achieve rapid and efficient technical development of the UMTS, five technical specification groups (TSG) have been created for determining the specification of the UMTS by considering the independent nature of the network elements and their operations.
Each TSG develops, approves, and manages the specification within a related region. Among these groups, the radio access network (RAN) group (TSG-RAN) develops the specifications for the functions, requirements, and interface of the UMTS terrestrial radio access network (UTRAN), which is a new radio access network for supporting W-CDMA access technology in the UMTS.
A related art UMTS network structure 1 is illustrated in FIG. 1. As shown, a mobile terminal, or user equipment (UE) 10 is connected to a core network (CN) 200 through a UMTS terrestrial radio access network (UTRAN) 100. The UTRAN 100 configures, maintains and manages a radio access bearer for communications between the UE 10 and the core network 200 to meet end-to-end quality of service requirements.
The UTRAN 100 includes a plurality of radio network subsystems (RNS) 110, 120, each of which comprises one radio network controller (RNC) 111 for a plurality base stations, or Node Bs 112. The RNC 111 connected to a given base station 112 is the controlling RNC for allocating and managing the common resources provided for any number of UEs 10 operating in one cell. One or more cells exist in one Node B. The controlling RNC 111 controls traffic load, cell congestion, and the acceptance of new radio links. Each Node B 112 may receive an uplink signal from a UE 10 and may transmit downlink signals to the UE 10. Each Node B 112 serves as an access point enabling a UE 10 to connect to the UTRAN 100, while an RNC 111 serves as an access point for connecting the corresponding Node Bs to the core network 200.
Among the radio network subsystems 110, 120 of the UTRAN 100, the serving RNC 111 is the RNC managing dedicated radio resources for the provision of services to a specific UE 10 and is the access point to the core network 200 for data transfer to the specific UE. All other RNCs 111 connected to the UE 10 are drift RNCs, such that there is only one serving RNC connecting the UE to the core network 200 via the UTRAN 100. The drift RNCs 111 facilitate the routing of user data and allocate codes as common resources.
The interface between the UE 10 and the UTRAN 100 is realized through a radio interface protocol established in accordance with radio access network specifications describing a physical layer (L1), a data link layer (L2) and a network layer (L3) described in, for example, 3GPP specifications. These layers are based on the lower three layers of an open system interconnection (OSI) model that is well known in communications systems.
A related art architecture of the radio interface protocol is illustrated in FIG. 2. As shown, the radio interface protocol is divided horizontally into a physical layer, a data link layer, and a network layer, and is divided vertically into a user plane for carrying data traffic such as voice signals and Internet protocol packet transmissions, and a control plane for carrying control information for the maintenance and management of the interface.
The physical layer (PHY) provides information transfer service to a higher layer and is linked via transport channels to a medium access control (MAC) layer. Data travels between the MAC layer and the physical layer via a transport channel. The transport channel is divided into a dedicated transport channel and a common transport channel depending on whether a channel is shared. Also, data transmission is performed through a physical channel between different physical layers, namely, between physical layers of a sending side (transmitter) and a receiving side (receiver).
The MAC layer of the second layer provides a service to an upper layer, namely, an RLC (Radio Link Control) layer, via a logical channel. The RLC layer supports reliable data transmissions, and performs a segmentation and concatenation function on a plurality of RLC service data units (RLC SDUs) delivered from an upper layer.
A radio resource control (RRC) layer located in a lowermost portion of the L3 layer is defined only in the control plane. The RRC manages the control of logical channels, transport channels, and physical channels with respect to establishment, reconfiguration and release of radio bearers (RBs). A radio bearer service refers to a service that the second layer (L2) provides for data transmission between the terminal and the UTRAN. In general, the establishment of a radio bearer refers to defining the protocol layers and the channel characteristics of the channels required for providing a specific service, as well as respectively setting substantial parameters and operation methods.
An MBMS is implemented in the UMTS system as follows. The MBMS refers to a method for providing a streaming or background service to multiple terminals by using a downlink-exclusive MBMS bearer service. One MBMS service is made up of one or more sessions, and MBMS data is transmitted to multiple terminals through the MBMS bearer service only when a session is ongoing.
The UTRAN 100 provides the MBMS bearer service to terminals using an RB. Two types of RBs used by the UTRAN 100 are a point-to-point RB and a point-to-multipoint RB. The point-to-point RB is a bi-directional RB, including a logical channel DTCH (Dedicated Traffic Channel), a transport channel DCH (Dedicated Channel) and a physical channel DPCH (Dedicated Physical Channel) or a physical channel SCCPCH (Secondary Common Control Physical Channel).
The point-to-multipoint RB is a unidirectional downlink RB, including a logical channel MTCH (MBMS Traffic Channel), a transport channel FACH (Forward Access Channel) and the physical channel SCCPCH as shown in FIG. 3. The MTCH is configured for every MBMS service provided in one cell and used to transmit user plane data of a specific MBMS service to multiple terminals.
FIG. 3 illustrates a channel mapping structure of the point-to-multipoint RB. A logical channel MCCH, which is a point-to-multipoint downlink channel, transmits MBMS-related control information. The MCCH is mapped to the transport channel FACH. The FACH is mapped to the physical channel SCCPCH. Only one MCCH exists in one cell.
FIG. 4 illustrates a structure of MAC layers of a mobile terminal and a UTRAN that handle an MBMS. A MAC-c/sh/m sublayer (hereinafter referred to as “MAC-c/sh/m”), as shown in FIG. 4, performs three types of functions.
First, the MAC-c/sh/m manages transport channels, such as a PCH (Paging Channel), the FACH and a RACH (Random Access Channel), to which common logical channels, such as a CCCH (Common Control Channel), a CTCH (Common Traffic Channel), a BCCH (Broadcast Control Channel) and a PCCH (Paging Control Channel) that every terminal in a cell region can receive are mapped. Second, the MAC-c/sh/m manages a transport channel DSCH (Downlink Shared Channel). Third, the MAC-c/sh/m manages the transport channel FACH to which the MBMS-exclusive logical channels MCCH and MTCH are mapped.
The MAC-c/sh/m of the UTRAN is located in an RNC. One MAC-c/sh/m exists per cell region. On the terminal side, one MAC-c/sh/m exists per terminal. A MAC-d sublayer (“MAC-d”), as shown in FIG. 4, manages dedicated logical channels DTCH and DCCH.
Referring to FIG. 4, an RRC layer respectively controls a MAC entity, such as the MAC-c/sh/m and the MAC-d through a MAC control SAP (Service Access Point). The RRC layer and the MAC layer exchange one or more primitives through the MAC control SAP. Primitives exchanged through the MAC control SAP include a primitive used for the RRC layer to control the MAC layer and a primitive used for the MAC layer to report to the RRC layer. Each primitive includes a parameter to be used by the RRC layer and the MAC layer.
FIG. 5 illustrates a radio protocol architecture in accordance with a related art MBMS selective combining method. As shown in FIG. 5, when receiving the same MBMS service from a plurality of cell regions, a terminal receives the same MBMS data through a plurality of physical channels SCCPCHs and combines the received MBMS data. In this respect, the MBMS data may be combined using methods such as selective combining and soft combining.
In soft combining, a physical layer of a receiving side, preferably the terminal, processes data received by one MAC-c/sh/m entity by combining respectively different physical channels.
In selective combining, as shown in FIG. 5, the terminal comprises a plurality of MAC-c/sh/m entities corresponding to each cell region, wherein each MAC-c/sh/m entity processes received MBMS data. The processed MBMS data of each MAC-c/sh/m entity is then combined in the RLC layer. Accordingly, to perform selective combining, the terminal and the UTRAN must have a plurality of MAC-c/sh/m entities corresponding to each cell region.
Assuming that a cell region (“cell”) in which the terminal is positioned is a current cell (cell #1) and a cell adjacent to the current cell is a neighboring cell (cell #2), the related art selective combining method makes the MAC-c/sh/m of the terminal for the cell #2, specifically, MAC-c/sh/m #2, receive a common channel other than the MTCH.
However, it has been realized that the reception of a common channel other than the MTCH from the neighboring cell and not from the current cell, namely, the reception of non-MBMS data from the neighboring cell, is practically an unnecessary operation. Such operation degrades efficiency of the overall communications system and wastes communication resources.